Efforts in the design of integrated circuits for radio frequency (RF) communication systems generally focus on improving performance, reducing cost or a combination thereof. One area of increasing interest relates to conversion of signals, such as from analog-to-digital, digital-to-analog or digital-to-digital. These types of conversion have benefited from the development and use of delta-sigma modulation.
Delta-sigma modulation is a technique used to generate a coarse estimate of a signal using a small number of quantization levels and a high sampling rate. Limiting a signal to a finite number of levels introduces “quantization noise” into the system. The effect of oversampling and the use of an integrator feedback-loop in delta-sigma modulation are effective in shifting noise, including quantization noise, to out-of-band frequencies. The noise shifting properties enables efficient use of subsequent filtering stages to remove noise and produce a more precise representation of the input.
In order to achieve increasing efficiency and precision in delta-sigma modulation, a delta-sigma modulator often must be operated at high sampling rates. For example, faster modulators can be fabricated using more expensive technologies, such as Silicon Germanium (SiGe) or Indium Phosphide (InP). These semiconductor technologies, however, tend to have limits in chip, size, number of transistors and/or are not cost effective in many applications due to their low yields and/or higher material costs
For wireless commercial applications, in particular, there is a need for a low cost converter having a high dynamic range and wide bandwidth.